The Siwalik Hills, also known as the Outer Himalayas, are the southernmost and youngest range of the Himalayan mountain system. They extend from the Indus River in Pakistan to the Brahmaputra Valley in India and traverse through several states of India viz., Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Uttar Pradesh, Bihar, West Bengal, Assam and Arunachal Pradesh. They were formed by the deposition of sediments carried by Himalayan rivers during the Miocene to Pleistocene epochs, and by post-Pleistocene sedimentation produced through weathering processes in lower-elevation areas. They are important for geography and competitive exams as they play a vital role in soil conservation, groundwater recharge and maintenance of ecological balance in the Himalayan region.
About Siwalik Hills
The Siwalik Hills, or Outer Himalayas, are the southernmost and youngest range of the Himalayan mountain system. They are about 2,400 km long (from the Indus River in Pakistan to the Brahmaputra Valley of India) and average between 10–50 km wide. The sedimentary Siwalik Hills were formed from the Miocene to Pleistocene by the downwash of Himalayan rivers. Less lofty than the Greater Himalaya and Lesser Himalaya, they are nevertheless crucial to safeguarding the Indo-Gangetic Plains, sustaining biodiversity, regulating river systems and providing ecosystem services related to forests. It is also known for fossiliferous deposits, diverse flora and fauna and wildlife sanctuaries.
Key Features and Location of the Siwalik Hills
- The youngest and further south, the Siwalik Hills is a part of the Outer Himalayas mountain system.
- They extend for approximately 2,400 km from the Indus River in Pakistan to the Brahmaputra Valley of India.
- Siwalik Hills are 10 km to 50 km in average width.
- Ranging from 600 metres up to 1,500 metres at most.
- The hills traverse Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Uttar Pradesh, Bihar, West Bengal, Assam & Arunachal.
- These were created from alluvial sediments laid down by rivers derived from the Greater Himalayas.
- The Main Boundary Thrust (MBT) separates the Siwalik Hills from the Lesser Himalayas.
- The Duns are fertile valleys found in the foothills, including the renowned Dehradun Valley.
- Dense forests are another feature of the region, which is very rich in biodiversity, and numerous wildlife sanctuaries and national parks abound here.
- The Siwalik Hills are not only crucial for soil conservation, groundwater recharge and river drainage for India bordering the north, but they also maintain ecological balance.
Siwalik Hills Biodiversity
The Siwalik Hills are among the most biodiverse regions of the Himalayan foothills, supporting tropical and subtropical forests, grasslands and riverine ecosystems. It is a biodiversity hotspot which supports Eastern Himalayan species such as the Asian elephant, Bengal tiger, leopard, Himalayan black bear, deer and thousands of bird species.
Flora of the Siwalik Hills
- Most of the Siwalik Hills are covered with tropical deciduous and subtropical forests, which represent one of the richest forest ecosystems in the lowland and hills of the central Himalaya region.
- The tree species of Sal (Shorea robusta) is the main one, while others such as Sheesham, Khair, Teak, Bamboo, as well as Semal and Chir Pine can be found.
- The Bhabar and Terai areas are dense grasslands of fertile regions, which provide habitat to different medicinal plant species.
- Riparian vegetation is found on river banks and near temporary rivers, acting as an important filter to prevent soil moisture loss and erosion.
- These various plants help create wildlife habitat, enhance groundwater recharge and support the sustainability of fauna.
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| Krishna River System | Sutlej River System |
Fauna of the Siwalik Hills
- The Siwalik Hills ecoregion is one of India’s major biodiversity hotspots, supporting high diversity and endemism among its flora and fauna.
- These forests are home to mammals like the Asian Elephant, Bengal Tiger, Leopard, Himalayan Black Bear, Sambar, Chital Deer (Axis) or Spotted Deer; Barking Deer (Muntjak); and Wild Boar.
- Besides this, the region also has Rhesus Macaques, Hanuman Langurs and plenty of birds like Hornbills, Peafowl, Eagles and Vultures.
- Famous global palaeontological sites include the Siwalik Fossil Beds, home to animal fossils from extinct lineages: Sivapithecus, Sivatherium, Megalochelys Atlas and even ancient elephants.
- Siwalik Hills have national parks and wildlife sanctuaries very important for wildlife conservation as well as endangered species protection.
- The region also supports reptiles such as the King Cobra, Indian Python, Monitor Lizard, and several turtle species.
